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ABSTRACT & COMMENTARY
By John C. Hobbins, MD
Professor, Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora
Dr. Hobbins reports no financial relationships relevant to this field of study.
SYNOPSIS: The findings in a recent study in which investigators evaluated the relative contributions of pre-pregnant weight, weight gain in pregnancy, and the presence of gestational diabetes on the rate of large-for-gestational age fetuses has shed light on how this true complication of pregnancy can be diminished.
SOURCE: Kim SY, et al. Association of maternal body mass index, excessive weight gain, and gestational diabetes mellitus with large-for-gestational age births. Obstet Gynecol 2014;123:737-744.
There has been a recent focus on downstream problems associated with pregnancies complicated by large-for-gestational age (LGA) fetuses. Since obesity is associated with LGA babies and the rate of obesity in the United States is still growing, a study has just surfaced to evaluate the effects of three variables — pre-pregnant weight, weight gain and pregnancy, and gestational diabetes (GDM) — on excessive fetal weight.1
The authors reviewed records from 2004 to 2008 from a Florida state hospital discharge database, as well as from birth certificates. Pre-pregnant body mass index (BMI) was recorded, as well as weight gain in pregnancy and infant weight at birth. The authors used the following guidelines for ideal weight gain in pregnancy: those with BMIs < 18.5 kg/m2 (underweight) 28-40 pounds; 18.5-25 kg/m2 (normal) 25-35 pounds; 25-30 kg/m2 (overweight) 15-25 pounds; > 30 kg/m2 (obese) 11-20 pounds. The authors further broke down obesity into three classes according to BMI: class I, 30-35 kg/m2; class II, 35-40 kg/m2; and class III, > 40 kg/m2. However, the ideal weight gain requirements were the same across all classes of obesity.
LGA, defined as a birth weight above the 90th percentile, occurred in 5.7% of women with normal BMI, acceptable weight gain, and no diabetes. This was compared with women at the other end of the BMI spectrum (class III obesity) who had excessive weight gain and GDM. These patients had a rate of LGA of 35.1%. An important finding was that if one considered each factor individually, the rate of LGA was 17.3% in GDM, 13.5% when there is excessive weight gain, and 12.6% in those who were overweight or obese.
Among races, overweight Pacific Islanders had the highest overall rate of LGA of 48%, and the lowest occurred in overweight Caucasians, with a rate of 22.8%. The most important finding was that across all ethnic groups, the greatest contribution to LGA was excessive weight gain, responsible for a 33.3-37.7% increase, compared to GDM, which only added 2-8% to the rate of LGA.
Other Alerts have focused on the obesity epidemic in the United States. Large babies often come from large mothers and there is a strong evidence to show that large babies have higher rates of hypoxia, birth injury,2 and are more likely to develop diabetes3 and to be obese themselves later in life.4 This in turn predisposes them to higher rates of asthma and even cancer.2
Recently it has become clear that some large babies are even more predisposed to later problems if they have more accumulated body fat than their counterparts of the same birth weight.5 This type of excessive fat accumulation can even be suspected in utero with 3-D ultrasound measurements of fractional thigh volumes — a method superior to the standard biometric formulas to estimate fetal weight (which does not take into account the percentage of adipose tissue responsible for their overall size).6
Despite the gloomy statistics on obesity, there is hope that this national trend and the escalating costs associated with health care needs of the progeny of overweight women actually can be tempered. This study shows that curtailing weight gain in pregnancy can make the biggest difference, and a program to get women between pregnancies down to a reasonable starting pre-pregnant weight can also be very effective. In fact, in the same month (April), a study in the American Journal of Obstetrics and Gynecology has shown that initiating a contraceptive program immediately after pregnancy is very effective in attaining the ideal 18-month interval between pregnancies,7 leaving ample time for overweight/obese women to drop their BMIs. Last, since obesity begets diabetes, the above steps will also diminish the incidence of LGA resulting from glucose intolerance.